Less Soak Time Saves Those upon the Line: Capture Times and Hooking Mortality of Sharks Caught on Bottom Longlines

The National Marine Fisheries Service is mandated by the Magnuson-Stevens Fishery Conservation and Management Act to implement effective annual catch limits and accountability measures to prevent overfishing. These requirements compel further research into alternative fishing practices that could reduce mortality of sharks (class Chondrichthyes) and allow fishers to release unwanted sharks to the water alive, while still effectively catching targeted species. We used hook timers and temperature-depth recorders aboard contracted vessels and participants in the National Marine Fisheries Service's Shark Research Fishery to collect hooking time and time-on-the-line data for 10 species of sharks that were commonly encountered in the fishery. A subset of standardized fishing sets compared the most popular circle hook and J-hook models. Over 60% of sharks were hooked within 4 h of hook soak time. The fastest to bite the hook was the Atlantic Sharpnose Shark Rhizoprionodon terraenovae and the slowest was the Dusky Shark Carcharhinus obscurus. Shark resilience to time on the longline varied among species, with Sandbar Shark C. plumbeus exhibiting the most resilience and Atlantic Sharpnose Shark the least. Shorter set soak times, approximately 2 h, would still maximize catch, while minimizing at-vessel mortality. The most frequently used circle hook model did not significantly reduce at-vessel mortality over large J-style hooks. The recent circle hook requirement will have little effect for fishers that previously used 12/0 J-hooks, but it may be beneficial by preventing the use of smaller J-hooks that are more likely to cause at-vessel mortality.

Automated summary

Research into alternative fishing practices to reduce shark mortality found that shorter set soak times can minimize vessel mortality while maximizing catch, with circle hooks not significantly reducing at-vessel mortality over J-hooks. The recent circle hook requirement may not impact fishers using 12/0 J-hooks, but could be beneficial in preventing the use of smaller J-hooks that are more likely to cause vessel mortality.